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  <script>
    // 使用for循环 - 求出班级里同学们平均年龄[15, 19, 21, 33, 18, 24]
    let arr = [15, 19, 21, 33, 18, 24]
    let sum = 0
    let ava= 0
    for(let i = 0;i<arr.length;i++) {
      sum += arr[i]
      ava = sum / arr.length
    }

    document.write(ava);

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